Polycrystalline silicon ingot casting method for lowering oxygen content at bottom of polycrystalline silicon ingot

Abstract

The invention discloses a polycrystalline silicon ingot casting method for lowering the oxygen content at the bottom of a polycrystalline silicon ingot. The method comprises the steps of 1 crucible bottom coating preparation, wherein coating spraying liquid preparation, spraying and drying are conducted; 2 loading, wherein a silicon material is loaded into a crucible with a bottom coating, the crucible loaded with the silicon material is put into a polycrystalline silicon ingot furnace, and the polycrystalline silicon ingot furnace is internally provided with a six-face heating device which comprises a bottom heater, a top heater and four side heater; 3 preheating; 4 melting, wherein the melting step comprises the following substeps of first-time heating, second-time heating and subsequent melting; 5 crystal growing; 6 annealing and cooling. According to the polycrystalline silicon ingot casting method for lowering the oxygen content at the bottom of the polycrystalline silicon ingot, the design is reasonable, simpleness and convenience are achieved, and the using effect is good; the bottom coating taking boron nitride as the main raw material is coated on the bottom of the crucible, the six-face heating device is adopted for heating, the oxygen content at the bottom of the crucible can be effectively lowered, hard points of a finished ingot product can be effectively reduced, and the quality of the finished ingot product can be improved.

Description

technical field [0001] The invention belongs to the technical field of polycrystalline silicon ingots, in particular to a polycrystalline silicon ingot casting method for reducing the oxygen content at the bottom of the polycrystalline silicon ingot. Background technique [0002] Photovoltaic power generation is one of the most important clean energy sources with great development potential. The key factors restricting the development of photovoltaic industry are low photoelectric conversion efficiency on the one hand and high cost on the other hand. Photovoltaic silicon wafers are the basic material for the production of solar cells and components. The purity of polysilicon used to produce photovoltaic silicon wafers must be above 6N (that is, the total content of non-silicon impurities is below 1ppm), otherwise the performance of photovoltaic cells will be greatly negative influences. In recent years, the production technology of polycrystalline silicon wafers has made r...

AI Technical Summary

Problems solved by technology

At present, in the solar polysilicon ingot casting process, the crucible spraying process used is Si 3 N 4 material as a spray material, but due to Si 3 N 4 The poor thermal conductivity and instability of the material itself make it easy to form hard spots during the ingot casting process, and the oxygen content at the bottom of the finished ingot is relatively high, which has a great impact on the quality of the product

At the same time, Si 3 N 4 Although the material can effectively isolate the reaction between the silicon liquid and the crucible, the Si 3 N 4 After reacting with silicon liquid, a red zone is formed, which is easy to introduce impurity Si 3 N 4 And form a hard point, which has a great influence on the quality of the finished ingot

[0004] In addition, the heaters used in the existing polysilicon ingot furnaces generally have a five-sided heating structure, that is, heaters are installed on the top of the crucible and outside the four side walls. This five-sided heating method heats up from top to bottom. Radiation, melting efficiency is low, and at the same time, the gas at the bottom of the crucible is difficult to get rid of, so that the oxygen content at the bottom of the finished ingot is relatively high

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